Switching device, drive and manufacturing methods for the same, integrated circuit device and memory device

ABSTRACT

Provided is a switching device including ion conducting part  4  having an ion conductor, first electrode  1  formed at a first gap away from ion conducting part  4,  second electrode  2  formed to be in contact with ion conducting part  4  and third electrode  3  formed at a second gap away from ion conducting part  4.  Second electrode  2  supplies metal ions to the ion conductor, or receives the metal ions from the ion conductor to precipitate metal corresponding to the metal ions.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/722,825, filed Jun. 26, 2007, which is a national stage ofInternational Application No. PCT/JP2005/023656, filed Dec. 22, 2005,claiming priority based on Japanese Patent Application No. 2004-376767,filed Dec. 27, 2004, the contents of all of which are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a switching device used in anintegrated circuit, drive and manufacturing methods for the same, anintegrated circuit device and a memory device.

BACKGROUND ART

Many integrated circuit devices are now used in electrical appliances.Many integrated circuit devices used in the electrical appliances areso-called “ASIC (Application Specific Integrated Circuit)” and dedicatedcircuits designed for particular electrical appliances. In these ASICs,because a cell (logic circuit such as an AND circuit and an OR circuit)is arranged and interconnected in manufacturing steps, a circuitconfiguration thereof can not be changed after manufacturing.

Recently, competition to develop electrical appliances has intensifiedand miniaturization continues to make progress. In these circumstances,a programmable logic circuit in which a circuit configuration thereofcan be changed by an electric signal even after manufacturing and whichcan realize many functions on single chip draws interest. Arepresentative example of a programmable logic circuit is a FPGA(Field-Programmable Gate Array) or a DRP (Dynamically ReconfigurableProcessor) etc.

The programmable logic circuit attracts attention because of thisfeature, but implementation of a programmable logic circuit to anelectric appliance has up to now been limited. The reason is asfollowing.

That is, in a conventional programmable logic circuit, there have beenpresented problems that a size of a switching device for interconnectinga logic cell (i.e. a unit logic circuit for assembling the programmablelogic circuit—the programmable logic circuit is configured byinterconnecting a plurality of the logic cells using the switchingdevice) is large, and on-resistance thereof is high. Then, in order toreduce the number of switching devices that have a large size and highon-resistance as much as possible, the conventional programmable logiccircuit is configured in a manner that logic cells having as manytransistors as possible are used to reduce the number of logic cells andthe number of switching devices which interconnect the logic cells. As aresult, the degree of freedom in combining logic cells was decreased,thus limiting functions which the programmable logic circuit couldprovide. That is, the size and the high on-resistance of the switchingdevice that was used in the programmable logic circuit, limitedfunctionality of the programmable logic circuit, thus limitingimplementation of the programmable logic circuit in electric appliances.

Then, in order to diversify functionality of the programmable logiccircuit and promote implementation in electric appliances, it isnecessary to reduce the size of the switching device for interconnectinglogic cells with each other and to decrease its on-resistance.

A switching device satisfying these requirements, which uses theconduction phenomenon of metal ions in an ion conductor (solid inside ofwhich ions can freely move) and electrochemical reaction, has beenproposed (hereinafter, called “metal atom migration switching device”).(For example, see Japanese Patent Laid-Open No. 2002-076325 and NationalPublication of International Patent Application No. 2002-536840).

It is known that a metal atom migration switching device is smaller thana semiconductor switching device that (that example, a MOSFET) is usedoften in conventional programmable logic and has a lower on-resistance.This metal atom migration switching device is widely divided into twotypes shown in FIGS. 1A and 1B.

FIG. 1A shows a metal atom migration switching device with a gap, andFIG. 1B shows a metal atom migration switching device without a gap. Themetal atom migration switching devices shown in FIGS. 1A and 1B both aremetal atom migration switching devices having two terminals.

The metal atom migration switching device with a gap shown in FIG. 1A(see Japanese Patent Laid-Open No. 2002-076325) is a metal atommigration switching device having two terminals which include an ionconducting part composed of an ion conductor (Ag₂S), a second electrode(Ag) for supplying metal ions (Ag+) to the ion conducting part, or forreceiving the metal ions (Ag+) from the ion conducting part toprecipitate metal (Ag) corresponding to the metal ions and formed to bein contact with the ion conducting part, and a first electrode (Pt)formed to have a gap with the ion conducting part. (Material shown FIG.1A and for each component described above is exemplary).

When a negative voltage relative to the second electrode (Ag) is appliedto the first electrode (Pt) as shown in FIG. 1A, electrons, afterpenetrating an energy barrier (tunneling) in the gap between the firstelectrode (Pt) and the ion conducting part, reach the surface of the ionconducting part from the first electrode (Pt) and reduce the metal ions(Ag+) near the surface of the ion conducting part, precipitating metal(Ag).

When the metal (Ag) is precipitated, in response to this, metal (Ag) inthe second electrode is oxidized to melt in the ion conducting part asmetal ions (Ag+), and thereby, balance between positive ions andnegative ions in the ion conducting part is maintained. When theprecipitated metal (Ag) on the surface of the ion conducting part growsto be in contact with the first electrode (Pt), the switching deviceenters a conduction (on) state (see the left drawing in FIG. 1A).

On the one hand, when a positive voltage relative to the secondelectrode (Ag) is applied to the first electrode (Pt), quite the reverseelectrochemical reaction occurs. As a result, the precipitated metal(Ag) leaves the first electrode (Pt) and the switching device enters anon conduction (off) state (see the right drawing in FIG. 1A). Inaddition, as an ion conductor, a semiconductor or an insulator (forexample, Ag₂S is an n-type semiconductor) may be used. However, in orderto operate as a switching device (to provide a conduction (on) state),it is desirable for the ion conductor to have a large contact area withthe second electrode and be formed comparatively thinly.

The metal atom migration switching device without a gap shown in FIG. 1B (see National Publication of International Patent Application No.2002-536840) is a metal atom migration switching device having twoterminals which includes an ion conducting part composed of an ionconductor (Cu₂S), a second electrode (Cu) for supplying metal ions (Cu+)to the ion conducting part, or for receiving the metal ions (Cu+) fromthe ion conducting part to precipitate metal (Cu) corresponding to themetal ions, and which is formed to be in contact with the ion conductingpart, and a first electrode (Ti) formed to be in contact with the ionconducting part (Material shown in FIG. 1B and for each componentdescribed above is exemplary).

When a negative voltage relative to the second electrode (Cu) is appliedto the first electrode (Ti) as shown in FIG. 1B, the metal ions (Cu+)near the contact surface between the ion conducting part and the firstelectrode (Ti) are reduced, precipitating metal (Cu) on the contactsurface between the ion conducting part and the first electrode (Ti).When the metal (Cu) is precipitated, in response to it, metal (Cu) inthe second electrode is oxidized to melt in the ion conducting part asmetal ions (Cu+), and thereby, balance between positive ions andnegative ions in the ion conducting part is maintained.

Generally, because the ion conductor (Cu₂S) of the ion conducting partis softer than the first electrode (Ti), the precipitated metal (Cu)grows toward the second electrode (Cu) in the ion conducting part. Whenthe precipitated metal (Cu) comes in contact with the second electrode(Cu), the switching device enters to a conduction (on) state (see theleft drawing in FIG. 1B).

On the other hand, when a positive voltage relative to the secondelectrode (Cu) is applied to the first electrode (Ti), quite the reverseelectrochemical reaction occurs. As a result, the precipitated metal(Cu) leaves the second electrode (Cu) and the switching device enters anon conduction (off) state (see the right drawing in FIG. 1B).

The two types of metal atom migration switching devices shown in FIGS.1A and 1B have differences in configuration and operation describedabove, but in both of them, due to the electrochemical reaction, themetal atoms in the second electrode move between the first electrode andthe second electrode as a precipitate to form a metal wire for making aconnection between the first electrode and second electrode (when in theconduction (on) state).

The two types of metal atom migration switching devices shown in FIGS.1A and 1B both are metal atom migration switching device each having twoterminals. Such a metal atom migration switching device having twoterminals has a problem of low electro-migration resistance.

Electro-migration means a phenomenon in which metal atoms collide withelectrons, that are flowing in the metal wires, and which are to bemoved in metal wires. In high temperature environments, the flow ofelectric current having a current density over a certain level ismaintained in a metal wire, due to movement of the metal atoms caused bythe electro-migration and a serious problem such as breakage of metalwires will occur.

As described above, in a metal atom migration switching device havingtwo terminals, metal atoms, after moving from the second electrode tothe first electrode as a precipitate due to the electrochemicalreaction, form a metal wire to connect between the first electrode andthe second electrode. To prevent electro-migration in this metal wire,it is necessary to increase the amount of precipitate to form a thickermetal wire and to decrease the electric current density of currentflowing in the metal wire.

However, in the metal atom migration switching device having twoterminals, it is not easy to increase the amount of precipitate to makethe metal wire thicker. This is because, to increase the amount ofprecipitate, it is necessary to increase the absolute value of thenegative voltage, relative to the second electrode, that is applied tothe first electrode. However, once the metal wire for making aconnection between the first electrode and the second electrode isformed, the voltage applied between the first electrode and the secondelectrode may contribute to causing a large amount of electric currentto flow, but it does not contribute to increasing the amount ofprecipitate to make the metal wire thicker. On the contrary, if thevoltage is increased to prevent electro-migration, a large amount ofcurrent flows in the metal wire, and thereby, more electro-migration maybe induced.

DISCLOSURE OF THE INVENTION

Therefore, an object of the present invention is to provide a switchingdevice that permits the amount of precipitate, that is used to form ametal wire to make a connection between a first and a second electrode,to be easily controlled, and therefore, has high electro-migrationresistance, a drive and manufacturing methods for the same, anintegrated circuit device and a memory device.

A switching device according to the present invention, in order toachieve the object described above, newly includes a third electrode forcontrolling the amount of precipitate. That is, the switching deviceaccording to the present invention is a metal atom migration switchingdevice having three terminals. Further, the switching device accordingto the present invention is a metal atom migration switching devicehaving a gap and three terminals on the base of the metal atom migrationswitching device with a gap shown in FIG. 1A.

Specifically, the switching device according to the present inventionincludes an ion conducting part having an ion conductor inside of whichmetal ions can freely move, a first electrode formed to have a first gapbetween the first electrode and the ion conducting part, a secondelectrode for supplying the metal ions to the ion conductor, or forreceiving the metal ions from the ion conductor to precipitate metalcorresponding to the metal ions and which is formed to be in contactwith the ion conducting part, and a third electrode formed to have asecond gap between the third electrode and the ion conducting part (seeFIG. 1A).

According to such a configuration, when a negative voltage relative tothe second electrode is applied to the first electrode, electrons thatpenetrate an energy barrier in the first gap (tunneling), electrons thatbecome thermally excited in an insulator provided in the first gap orelectrons created from impurities or defects in the insulator, reach asurface of the ion conducting part and reduce the metal ions near thesurface of the ion conducting part, thus precipitating metal in thesecond electrode.

In response to this metal precipitation, the metal in the secondelectrode is oxidized to melt in the ion conducting part as metal ions,thus maintaining a balance between positive ions and negative ions inthe ion conducting part. The precipitated metal on the surface of theion conducting part grows to be in contact with the first electrode,thus providing a conduction (on) state of the switching device.

On the contrary, when a positive voltage relative to the secondelectrode is applied to the first electrode, quite the reverseelectrochemical reaction occurs. As a result, the precipitated metalmelts to allow the first electrode and the switching device enters a nonconduction (off) state. The operation described above is basically thesame as the operation in the metal atom migration switching devicehaving two terminals shown in FIG. 1A.

Further, when a negative voltage relative to the second electrode isapplied to the third electrode, or when a positive voltage relative tothe second electrode is applied to the third electrode, the operation,also, is basically the same. At this time, after a metal wire composedof a precipitate connects between the first electrode and the secondelectrode, a predetermined voltage relative to the second electrode isapplied to the third electrode, and thereby, the amount of precipitateand size of the metal wire dependent on it can be controlled. This isbecause the voltage applied to the third electrode hardly contributes toan increase in the electric current flowing in the metal wire thatconnects between the first electrode and the second electrode, but itcontributes to an increase in the amount of precipitate. Therefore, bycontrolling the voltage applied to the third electrode, the size of themetal wire composed of the precipitate is allowed to become larger, andelectro-migration resistance can be enhanced thereby.

In the switching device according to the present invention, the thirdelectrode is provided and a voltage applied to this third electrode iscontrolled, and the size of the metal wire composed of the precipitateto connect the first electrode and the second electrode is controlledthereby. Therefore, there is provided the advantage thatelectro-migration can be prevented, which has been a problem for metalatom migration switching devices having two terminals.

Moreover, the switching device according to the present invention hasthe following advantages, because it has a configuration based on ametal atom migration switching device having a gap.

In the metal atom migration switching device having a gap, compared tothe metal atom migration switching device without a gap, it is easy toadjust a switching voltage (voltage required for switching between an“on” state and an “off” state). This is because the material between thefirst electrode and the second electrode is limited to an ion conductorin the metal atom migration switching device without a gap, but on thecontrary, in the metal atom migration switching device with a gap, avacuum, a gas or an insulator may be used for the material. Moreover, inaddition to this, more freedom in designing the structure between thefirst electrode and the second electrode may be provided. These reasons,just as explained above, may also apply to the three-terminal type ofthe switching device. Therefore, a metal atom migration switching devicehaving a gap and three terminals according to the present invention hasan advantage in that it is easier to adjust the switching voltage bycontrolling the voltage applied to the first electrode and the voltageapplied to the third electrode, compared to a metal atom migrationswitching device without a gap having three terminals.

Further, in a metal atom migration switching device without a gap,because ionic conductance of the ion conductor between the firstelectrode and the second electrode is large and energy required for theelectrochemical reaction of the ion conductor is small, the switchingvoltage tends to be too low. Therefore, ensuring consistency of theswitching voltage with the operational voltage level of existingintegrated circuit devices becomes a problem.

However, in a metal atom migration switching device with a gap, such aproblem does not arise. This is because, in a metal atom migrationswitching device with a gap, the factor determining the switchingvoltage is not the ionic conductance or the energy needed for theelectrochemical reaction, but the energy for exciting electrons whichwill reduce metal ions in the ion conductor. This reason, just asexplained above, also applies to the three-terminal type, and so, in ametal atom migration switching device having a gap and three terminalsaccording to the present invention, which differs from a metal atommigration switching device without a gap and having three terminals, theproblem is not likely to occur in which the voltage applied to the firstelectrode and the switching voltage applied to the third electrode aretoo low.

BRIEF DESCRIPTION OF THE DRAWINGS

[Fig. 1A]

FIG. 1A is a schematic diagram illustrating a configuration andoperation of a metal atom migration switching device having a gap andtwo terminals.

[Fig. 1B]

FIG. 1B is a schematic diagram illustrating a configuration andoperation of a metal atom migration switching device without a gap andhaving two terminals.

[Fig. 2A]

FIG. 2A is a schematic diagram illustrating a configuration of a firstembodiment of a metal atom migration switching device having a gap andthree terminals according to the present invention.

[Fig. 2B]

FIG. 2B is a schematic diagram illustrating growth of a precipitate forforming a metal wire between a first electrode and a second electrodeshown in FIG. 2A.

[Fig. 3A]

FIG. 3A is a diagram illustrating one example of a drive method for themetal atom migration switching device having a gap and three terminalsshown in FIG. 2A, and also a schematic diagram illustrating growth ofthe precipitate that forms the metal wire between the first electrodeand the second electrode, when a negative voltage relative to the secondelectrode is applied to the first electrode.

[Fig. 3B]

FIG. 3B is a diagram illustrating one example of a drive method for themetal atom migration switching device having a gap and three terminalsshown in FIG. 1A, and also a schematic diagram illustrating an increasein size of the metal wire, when a negative voltage relative to thesecond electrode is applied to a third electrode.

[Fig. 4A]

FIG. 4A is a side sectional view illustrating manufacturing steps for ametal atom migration switching device having a gap and three terminalsaccording to the present invention.

[Fig. 4B]

FIG. 4B is a side sectional view illustrating manufacturing steps for ametal atom migration switching device having a gap and three terminalsaccording to the present invention.

[Fig. 5A]

FIG. 5A is a schematic diagram illustrating a configuration of a secondembodiment of a metal atom migration switching device having a gap andthree terminals according to the present invention.

[Fig. 5B]

FIG. 5B is a schematic diagram illustrating growth of a precipitate forforming a metal wire between a first electrode and a second electrodeshown in FIG. 5A.

[Fig. 6A]

FIG. 6A is a schematic diagram illustrating a configuration of a thirdembodiment of a metal atom migration switching device having a gap andthree terminals according to the present invention.

[Fig. 6B]

FIG. 6B is a schematic diagram illustrating growth of a precipitate forforming a metal wire between a first electrode and a second electrodeshown in FIG. 6A.

[Fig. 7A]

FIG. 7A is a schematic diagram illustrating a configuration of a fourthembodiment of a metal atom migration switching device having a gap andthree terminals according to the present invention.

[Fig. 7B]

FIG. 7B is a schematic diagram illustrating growth of a precipitate forforming a metal wire between a first electrode and a second electrodeshown in FIG. 7A.

[Fig. 8A]

FIG. 8A is a schematic diagram illustrating a configuration of a fifthembodiment of a metal atom migration switching device having a gap andthree terminals according to the present invention.

[Fig. 8B]

FIG. 8B is a schematic diagram illustrating growth of a precipitateforming a metal wire between a first electrode and a second electrodeshown in FIG. 8A.

[Fig. 9A]

FIG. 9A is a schematic diagram illustrating a configuration of a sixthembodiment of a metal atom migration switching device having a gap andthree terminals according to the present invention.

[Fig. 9B]

FIG. 9B is a schematic diagram illustrating growth of a precipitate forforming a metal wire between a first electrode and a second electrodeshown in FIG. 9A.

[Fig. 10A]

FIG. 10A is a schematic diagram illustrating a configuration of aseventh embodiment of a metal atom migration switching device having agap and three terminals according to the present invention.

[Fig. 10B]

FIG. 10B is a schematic diagram illustrating growth of a precipitate forforming a metal wire between a first electrode and a second electrodeshown in FIG. 10A.

[Fig. 11A]

FIG. 11A is a schematic diagram illustrating a configuration of aneighth embodiment of a metal atom migration switching device having agap and three terminals according to the present invention.

[Fig. 11B]

FIG. 11B is a schematic diagram illustrating growth of a precipitate forforming a metal wire between a first electrode and a second electrodeshown in FIG. 11A.

BEST MODE FOR CARRYING OUT THE INVENTION

As described above, the metal atom migration switching device accordingto the present invention is a metal atom migration switching devicehaving a gap and three terminals which includes an ion conducting parthaving an ion conductor inside of which metal ions can freely move, afirst electrode positioned at a first gap away from the ion conductingpart, a second electrode for supplying the metal ions to the ionconductor, or for receiving the metal ions from the ion conductor toprecipitate metal corresponding to the metal ions, and which is formedto be in contact with the ion conducting part, and a third electrodepositioned at a second gap away from the ion conducting part.

Now, the first to eighth embodiments of a metal atom migration switchingdevice according to the present invention will be briefly describedhereinafter.

In the first and second embodiments, a metal atom migration switchingdevice according to the present invention will be described in relationto a basic configuration, a drive method and a manufacturing method.

The first embodiment (see FIG. 2A) is an example in which the first gapprovided between the ion conducting part and the first electrode, andthe second gap provided between the ion conducting part and the thirdelectrode are filled with a vacuum or a gas.

Here, when a negative voltage relative to the second electrode isapplied to the first electrode or to the third electrode, electronswhich reach the surface of the ion conducting part and reduce the metalions included in the ion conductor to precipitate metal are theelectrons which penetrated the energy barrier in the first gap or thesecond gap.

The second embodiment (see FIG. 5A) is an example in which the first gapprovided between the ion conducting part and the first electrode, andthe second gap provided between the ion conducting part and the thirdelectrode are provided with an insulator.

In this case, when a negative voltage relative to the second electrodeis applied to the first electrode or the third electrode, electronswhich reach the surface of the ion conducting part and reduce the metalions included in the ion conductor to precipitate the metal are theelectrons that penetrate the energy barrier in the first gap or thesecond gap, are the ones that thermally excited in the insulator, andare the ones that were created from impurities or defects in theinsulator.

The third to fifth embodiments are examples which, in addition to themetal atom migration switching device shown in the first embodiment orthe second embodiment, further include a component for limiting thedirection in which the precipitate growing on the surface of the ionconducting part extends, to the direction toward the first electrode.

In the third embodiment (see FIG. 6A), a block layer formed of dense,hard material is provided on the surface of the ion conducting part onthe side of the third electrode, and thereby, the precipitate growing onthe surface of the ion conducting part is blocked from extending towardthe third electrode, and the direction in which the precipitate canextend is limited to the direction toward the first electrode.

In the fourth embodiment (see FIG. 7A), the thickness of the gapprovided between the ion conducting part and the third electrode isformed to be thinner at the region of the ion conducting part on theside of the first electrode than at the other region, and so, theelectric field strength formed by a voltage relative to the secondelectrode applied to the third electrode becomes most powerful at thisregion that has a thinner gap thickness. Therefore, the direction inwhich the precipitate extends is limited to the direction toward thefirst electrode.

The fifth embodiment (see FIG. 8A), similarly to the second embodiment,is an example in which the first gap and the second gap are providedwith an insulator. However, the insulator, at a region between the ionconducting part and the first electrode, has a lower resistivity than atthe other region. As configured in this way, when a negative voltagerelative to the second electrode is applied to the third electrode,electrons reaching the surface of the ion conducting part areconcentrated on the ion conducting part on the side of the firstelectrode, and thereby, the direction in which the precipitate growingon the surface of the ion conducting part extends can be limited to thedirection toward the first electrode.

The sixth and seventh embodiments are examples which, in addition to themetal atom migration switching device shown in the first embodiment orthe second embodiment, further include a component for limiting thedirection in which the precipitate growing on the surface of the ionconducting part extends, to the direction toward the first electrode,and include a component for reducing the on-resistance by directlyconnecting the first electrode and the second electrode with the metalwire formed of the precipitate without the ion conducting part that hasa smaller electrical conductivity than that of metal.

In the sixth embodiment (see FIG. 9A), the second electrode composed ofdense, hard material is laminated onto the surface of the ion conductingpart on the side of the third electrode. This prevents the precipitate,growing on the surface of the ion conducting part, from extending in thedirection toward the third electrode, and limits the growth direction ofthe precipitate to the direction toward the first electrode. Further,because the second electrode is laminated onto the ion conducting part,as the precipitate precipitated on the surface of the ion conductingpart grows, it comes into contact with the second electrode. Therefore,without the ion conducting part, the first electrode and the secondelectrode are electrically connected to each other, thus reducing theon-resistance.

In the seventh embodiment (see FIG. 10A), the ion conducting part islaminated onto the second electrode and a block layer composed of dense,hard material is formed on the surface of the ion conducting part on theside of the third electrode. This prevents the precipitate, growing onthe surface of the ion conducting part, from extending in the directiontoward the third electrode, and limits the growth direction of theprecipitate to the direction toward the first electrode. Further,because the ion conducting part is laminated onto the second electrode,as the precipitate precipitated on the surface of the ion conductingpart grows, it comes into contact with the second electrode. Therefore,without the ion conducting part, the first electrode and the secondelectrode are electrically connected to each other, thus reducing theon-resistance.

The eighth embodiment (see FIG. 11A) is a metal atom migration switchingdevice having a gap and three terminals which includes an ion conductingpart having an ion conductor inside of which metal ions can freely move,a first electrode formed on the ion conducting part to be in contactwith the ion conducting part, a second electrode positioned on the ionconducting part at a predetermined distance away from the firstelectrode, for supplying the metal ions to the ion conductor, orreceiving the metal ions from the ion conductor to precipitate metalcorresponding to the metal ions, and formed to be in contact with theion conducting part, and a third electrode formed at a gap with the ionconducting part.

The metal atom migration switching device of the eighth embodiment isdifferent from the metal atom migration switching devices shown in thefirst to seventh embodiments, and it is configured so that the firstelectrode is in contact with the ion conducting part. However, since thefirst electrode and the second electrode are formed on the ionconducting part at a predetermined distance from each other, theprecipitate for forming the metal wire to connect the first electrodeand the second electrode is not formed inside the ion conducting part asis the case of the metal atom migration switching device without a gap,but it is formed on a surface of the ion conducting part lying betweenthe first electrode and the second electrode. In the case where theprecipitate is formed on the surface of the ion conducting part in thisway, by applying a voltage to the third electrode positioned at the gapaway from the ion conducting part, the amount of the precipitate and thesize of the metal wire depending on it can be controlled. Although thefirst electrode is in contact with the ion conducting part, the metalatom migration switching device of the eighth embodiment, may beconsidered to be the metal atom migration switching device with a gap.

Now, the first to eighth embodiments of the metal atom migrationswitching device according to the present invention will be hereinafterdescribed with reference to the accompanying drawings.

First Embodiment

FIG. 2A is a schematic diagram illustrating a configuration of a firstembodiment of a metal atom migration switching device having a gap andthree terminals according to the present invention. FIG. 2B is aschematic diagram illustrating growth of a precipitate for forming ametal wire between a first electrode and a second electrode shown inFIG. 2A.

As shown in FIG. 2A, the metal atom migration switching device of thefirst embodiment is configured in a manner that ion conducting part 4composed of an ion conductor (Cu₂S) is formed on insulating substrate 6(SiO₂), and second electrode 2 for supplying metal ions (Cu+) to ionconducting part 4, or for receiving the metal ions (Cu+) from ionconducting part 4 to precipitate metal (Cu) that correspond to the metalions is formed on substrate 6 to be in contact with ion conducting part4.

Further, on substrate 6, first electrode 1 (Pt) is formed at a first gapwith ion conducting part 4. Moreover, on substrate 6, third electrode 3(Pt) is formed at a second gap with ion conducting part 4. The first gapand the second gap form a part of gap 5, respectively.

In the first embodiment, gap 5 may be a vacuum or may be filled with agas. The first gap and the second gap have a thickness of about 1 nm toabout 10 nm.

For the ion conductor of ion conducting part 4, Cu₂S, compounds ofchalcogen elements (O, S, Se, Te) and metal, insulators includingsilicon (silicon oxide, silicon nitride, silicon oxynitride), perovskiteoxides (ABO₃, A: Mg, Ca, Sr, Ba, B: Ti) etc. may be used.

For the metal of second electrode 2, Cu, Ag, Pb etc. may be used.

For the material of first electrode 1 and third electrode 3, Pt, metalhaving a high-melting point (W, Ti, Ta, Mo), silicide (titaniumsilicide, cobalt silicide, molybdenum silicide) etc. may be used.

Next, operation of the metal atom migration switching device of thefirst embodiment will be described.

For example, when a negative voltage relative to second electrode 2 isapplied to first electrode 1, electrons which penetrated an energybarrier in the first gap between first electrode 1 and ion conductingpart 4 reach a surface of ion conducting part 4 and reduce metal ions(Cu+) near the surface of ion conducting part 4, precipitating the samemetal (Cu) as material of second electrode 2. In response toprecipitation of the metal, the metal (Cu) of second electrode 2 isoxidized to melt in ion conducting part 4 as the metal ions (Cu+), andthereby, balance between positive ions and negative ions in ionconducting part 4 is maintained. When the precipitated metal that isprecipitated on the surface of ion conducting part 4 grows to be incontact with first electrode 1, the metal atom migration switchingdevice enters a conduction (on) state (see FIG. 2B). On the one hand,when a positive voltage relative to second electrode 2 is applied tofirst electrode 1, quite the reverse electrochemical reaction describedabove occurs. As a result, the precipitated metal melts to separate fromfirst electrode 1, and the metal atom migration switching device entersa non conduction (off) state. (The operation described above isbasically the same as the operation of the metal atom migrationswitching device having a gap and two terminals shown in FIG. 11A).

Further, when a negative voltage relative to second electrode 2 isapplied to third electrode 3, or when a positive voltage relative tosecond electrode 2 is applied to third electrode 3, operation is alsobasically the same. At this time, even after the metal wire composed ofprecipitate 7 shown in FIG. 3B electrically connects first electrode 1and second electrode 2, a voltage relative to second electrode 2 isapplied to third electrode 3, and thereby, the amount of precipitate 7and the size of the metal wire dependent on it can be controlled. Thisis because the voltage applied to third electrode 3 can hardlycontribute to an increase in electric current that flows in the metalwire for connecting first electrode 1 and second electrode 2, but it maycontribute to an increase in the amount of precipitate 7.

Therefore, by controlling the voltage relative to second electrode 2applied to third electrode 3, the size of the metal wire composed ofprecipitate 7 is allowed to be larger, and electro-migration resistancecan be enhanced thereby.

FIG. 3A is a view illustrating one example of a drive method for themetal atom migration switching device having a gap and three terminalsshown in FIG. 2A, and is also a schematic diagram illustrating growth ofthe precipitate that forms the metal wire between the first electrodeand the second electrode, when a negative voltage relative to the secondelectrode is applied to the first electrode. Further, FIG. 3B is a viewillustrating one example of a drive method for the metal atom migrationswitching device having a gap and three terminals shown in FIG. 1A, andis also a schematic diagram illustrating an increase in the size of themetal wire, when a negative voltage relative to the second electrode isapplied to the third electrode.

As shown in FIG. 3A, by applying a negative voltage relative to secondelectrode 2 to first electrode 1, ion conducting part 4 and firstelectrode 1 are connected to each other with precipitate 7. Next, asshown in FIG. 3B, growth of precipitate 7 is promoted by applying anegative voltage relative to second electrode 2 to third electrode 3,thus enlarging the size of the metal wire composed of precipitate 7.Subsequently, application of a negative voltage or a positive voltagerelative to second electrode 2 to third electrode 3 causes precipitate 7to come into contact with first electrode 1 or to leave first electrode1, and thereby, the on/off operation of the metal atom migrationswitching device can be controlled.

In addition, in FIG. 3A, precipitate 7 grows due to the application of anegative voltage relative to second electrode 2 to first electrode 1,but, if it can be assured that precipitate 7 grows only in the directiontoward first electrode 1, the application of a negative voltage relativeto second electrode 2 to third electrode 3 may grow precipitate 7. Forexample, in the third to seventh embodiments described below, aconfiguration in which the growth direction of the precipitate islimited to the direction toward first electrode 1 is adopted. Therefore,by adopting such a configuration, a method for growing precipitate 7using the application of a negative voltage relative to second electrode2 to third electrode 3 is effective. Similarly, also in the eighthembodiment described below, there is shown a method in which the growthdirection of the precipitate is limited between the first electrode andthe second electrode, and so, by adopting this configuration, a methodfor growing precipitate 7 using the application of a negative voltagerelative to second electrode 2 to third electrode 3 is effective.

Next, a method for manufacturing a metal atom migration switching deviceof the first embodiment will be described.

First, photoresist is coated on substrate 6 (SiO₂), and an opening ofthe photoresist is formed on a formation area of first electrode 1 byultraviolet irradiation and development processing. Next, a Pt film toform first electrode 1 is deposited and first electrode 1 having athickness of about 1 nm to 100 nm is formed using the liftoff method.According to similar procedures, ion conducting part 4 (Cu₂S) having athickness of about 1 nm to 100 nm is formed, and further, secondelectrode 2 (Cu) having a thickness of about 1 nm to 100 nm is formed.In addition, a distance of 1 nm to 10 nm is provided between ionconducting part 4 and first electrode 1 (for forming the first gap).Next, a resist pattern is provided so as to cover ion conducting part 4,first electrode 1 and second electrode 2. At this time, the resist isformed on ion conducting part 4 to have a thickness of 1 nm to 10 nm(for forming the second gap).

Next, third electrode 3 is formed on this resist. After formation ofthird electrode 3, the first gap between ion conducting part 4 and firstelectrode 1, and the second gap between ion conducting part 4 and thirdelectrode 3 are formed by removing the resist using an organic solventsuch as acetone. In addition, the first gap and the second gap may befilled with a gas such as air.

In manufacturing the metal atom migration switching device of the firstembodiment, it is difficult to control the thickness of the first gapbetween ion conducting part 4 and first electrode 1.

FIGS. 4A and 4B show manufacturing procedures for forming the first gapto have a desired thickness.

First, on substrate 6, a Pt film to form first electrode 1 is grown to athickness of about 100 nm using a sputtering method (FIG. 4A(a)). Next,this Pt film is processed by lithographic technique and dry etchingtechnology, forming first electrode 1. Next, insulating film 9 (SiO₂) isgrown to a thickness of about 10 nm entirely on substrate 6 includingfirst electrode 1 (FIG. 4A(b)).

Next, insulating film 9 is removed using an anisotropic dry etchingmethod, with a side wall part of first electrode 1 being left behind(FIG. 4A(c)).

Next, ion conductor film 10 (Cu₂S) is grown to a thickness of about 50nm on substrate 6 so as to cover first electrode 1 using a laserablation method (FIG. 4A(d)).

Next, ion conductor film 10 is removed using anisotropic dry etchingmethod, while only the part of insulating film 9 that was left behind onthe side wall part of first electrode 1 is left behind (FIG. 4A(e)). Atthis time, ion conductor film 10 shown in the right side of FIG. 4A(e)becomes ion conducting part 4.

Next, second electrode 2 composed of a Cu film having a thickness ofabout 50 nm is formed using a liftoff method (FIG. 4B(f)).

Next, insulating film 11 (SiO₂) having a thickness of about 20 nm isgrown entirely on substrate 6 to cover first electrode 1 (FIG. 4B(g)).

Next, a Pt film having a thickness of about 100 nm is formed to coverinsulating film 11, and this Pt film is processed by a lithographictechnique and dry etching technology, forming third electrode 3 (FIG.4B(h)).

Finally, insulating film 9 and insulating film 11 are removed using awet etching method, respectively, forming gap 5 (FIG. 4B(i)). Gap 5 maybe filled with a gas.

According to the manufacturing method described above, because thethickness of the first gap between ion conducting part 4 and firstelectrode 1 can be controlled by the thickness of insulating film 9 thatis formed in the step shown in FIG. 4A(b)), the thickness of the firstgap can be easily controlled.

Second Embodiment

FIG. 5A is a schematic diagram illustrating a configuration of a secondembodiment of a metal atom migration switching device having a gap andthree terminals according to the present invention. FIG. 5B is aschematic diagram illustrating growth of a precipitate for forming ametal wire between a first electrode and a second electrode shown inFIG. 5A.

In the metal atom migration switching device of the first embodiment isconfigured such that gap 5 is filled with the vacuum or a gas as shown,but the metal atom migration switching device of the second embodimentis configured so that gap 5 includes an insulator (for example, a resistor SiO₂). According to this difference in configuration, the followingdifference in operation of the metal atom migration switching device isgenerated. That is, in the first embodiment, when a negative voltagerelative to second electrode 2 is applied to first electrode 1 or tothird electrode 3, electrons which reach the surface of ion conductingpart 4 to reduce the metal ions included in ion conducting part 4 arethe ones which penetrated the energy barrier in the first gap or thesecond gap (tunneling).

On the one hand, in the second embodiment, since gap 5 includes theinsulator (solid), the electrons which reach the surface of ionconducting part 4 to reduce the metal ions included in ion conductingpart 4 are not limited to the ones which penetrated the energy gap inthe gap (tunneling), but include the ones that were thermally excited inthe insulator and the ones that were created from impurities and defectsin the insulator (here, the insulator means a substance having a bandgap at a distance, including a semiconductor).

As stated above, since the second embodiment uses the electrons in theinsulator, it is not necessary to make the first gap and the second gapas thin as in the first embodiment. It may be sufficient that thethickness of the first gap and the second gap is about 1 nm to 100 nm.

A method for manufacturing the metal atom migration switching device ofthe second embodiment can only be provided by omitting the step ofremoving the insulator (FIG. 4B(i)) from the steps shown in the firstembodiment.

As shown in the first and second embodiments, the metal atom migrationswitching device according to the present invention is the metal atommigration switching device with a gap, and so, the material for fillinggap 5 can be comparatively freely changed. Therefore, it has thefollowing advantages.

In the metal atom migration switching device with a gap, compared to themetal atom migration switching device without a gap, it is easy toadjust the switching voltage (voltage needed for switching between an onstate and an off state). This is because the material between the firstelectrode and the second electrode is limited to an ion conductor in themetal atom migration switching device without a gap, but, on thecontrary, in the metal atom migration switching device with a gap, thematerial can be selected from among a vacuum, a gas and an insulatoretc., providing higher freedom in the design of a structure between thefirst electrode and the second electrode. This reason, just as explainedabove, also applies to the three-terminal type, and it is easier toadjust the switching voltage applied to the first electrode or the thirdelectrode in the metal atom migration switching device having a gap andthree terminals according to the present invention than in the metalatom migration switching device without a gap and having threeterminals.

Further, in the metal atom migration switching device without a gap, theion conductor between the first electrode and the second electrode has alarge ionic conductance and needs small amount of energy for theelectrochemical reaction in the ion conductor, and so, the switchingvoltage tends to be too small. Therefore, there arises the problem ofconsistency with operational voltages in existing integrated circuitdevices. On the one hand, in the metal atom migration switching devicewith a gap, such a problem is not likely to occur. This is because, inthe metal atom migration switching device having a gap, the factor thatdetermines the switching voltage is not the ionic conductance or theenergy that is needed for the electrochemical reaction, but is energythat is needed to excite electrons which will reduce metal ions in theion conductor. This reason, just as explained above, applies to thethree-terminal type, and so, in the metal atom migration switchingdevice having a gap and three terminals according to the presentinvention, that is different from the metal atom migration switchingdevice without a gap and having three terminals, the problem is likelynot to occur that the switching voltage applied to the first electrodeor the third electrode is too low.

In addition, when the insulator is used for ion conducting part 4, aninsulator having a lower ionic conductance than that of an insulatorused for ion conductor 4 is preferably used for gap 5. For example, whenSiO₂ is used for ion conducting part 4, SiN having a lower ionicconductance than that of SiO₂ is preferably used for the insulator ingap 5.

Third Embodiment

FIG. 6A is a schematic diagram illustrating a configuration of a thirdembodiment of a metal atom migration switching device having a gap andthree terminals according to the present invention. FIG. 6B is aschematic diagram illustrating growth of a precipitate for forming ametal wire between a first electrode and a second electrode shown inFIG. 6A.

As shown in FIG. 6A, the metal atom migration switching device of thethird embodiment is different from the metal atom migration switchingdevice of the first embodiment in the point that, block layer 8 isformed, on a surface of ion conducting part 4 on the side of thirdelectrode 3. For block layer 8, dense, hard material such as SiO₂ ispreferably used.

This difference generates the following difference in operation of themetal atom migration switching device. That is, since block layer 8 iscomposed of dense, hard material, precipitate 7 does not grow toward theside of block layer 8 of ion conducting part 4 and does not extend inthe direction toward third electrode 3. As a result, the growthdirection of precipitate 7 is limited to the direction from ionconducting part 4 toward first electrode 1.

This provides the advantage that wrong operation of the metal atommigration switching device (for example, an operation in whichprecipitate 7 extends in the direction toward third electrode 3 to be incontact with third electrode 3) can be prevented. Further, as describedabove, it is advantageous, when the drive method, in which a voltagerelative to second electrode 2 is applied to third electrode 3, isadopted.

A method for manufacturing the metal atom migration switching device ofthe third embodiment is provided by adding a step of forming block layer8 using a liftoff method between the formation step (liftoff method) forion conducting part 4 shown in FIG. 4A(e) and the formation step(liftoff method) for second electrode 2 shown in FIG. 4B(f).

In addition, the metal atom migration switching device of the thirdembodiment may also include an insulator in gap 5, similarly to thesecond embodiment.

Fourth Embodiment

FIG. 7A is a schematic diagram illustrating a configuration of a fourthembodiment of a metal atom migration switching device having a gap andthree terminals according to the present invention. FIG. 7B is aschematic diagram illustrating growth of a precipitate for forming ametal wire between a first electrode and a second electrode shown inFIG. 7A.

As shown in FIG. 7A, the metal atom migration switching device of thefourth embodiment is configured so that a thickness of gap 5 providedbetween ion conducting part 4 and third electrode 3 is formed to bethinner at the region of ion conducting part 4 on the side of firstelectrode 1 than at another region. That is, the thickness of a regioncorresponding to the first gap between ion conducting part 4 and firstelectrode 1 in the first gap is formed thinner than that of the otherregion including the second gap. Therefore, it is different from themetal atom migration switching device of the first embodiment in thepoint that third electrode 3 is formed in a convex shape at this regionin which gap 5 is thinner.

This difference generates a difference in operation of the metal atommigration switching device as described below. That is, when a negativevoltage relative to second electrode 2 is applied to third electrode 3,the electric field strength that is created by a gate voltage becomespowerful especially at the first gap between ion conducting part 4 andfirst electrode 1. Therefore, more electrons which will reduce the metalions near the surface of ion conducting part 4 reach the surface of ionconducting part 4 on the side of first electrode 1. As a result, thedirection in which precipitate 7 extends is limited to the directionfrom ion conducting part 4 toward first electrode 1 (see FIG. 7B).Therefore, there is provided the advantage that wrong operation of themetal atom migration switching device (for example, an operation inwhich precipitate 7 extends in the direction toward third electrode 3 tobe in contact with third electrode 3) can be prevented. Further, asdescribed above, it is advantageous, when the drive method, in which avoltage relative to second electrode 2 is applied to third electrode 3,is adopted.

A method for manufacturing the metal atom migration switching device ofthe fourth embodiment is provided by adding a step, to the step shown inFIG. 4B(g), for processing the resist (or insulating film) for forminggap 5 to be in a convex shape. As an example, in relation to the casewhere gap 5 includes resist, the method for manufacturing the metal atommigration switching device of the fourth embodiment will be describedhereinafter, but it also applies to the case where insulating film isused.

According to the manufacturing method of this embodiment, afterformation of second electrode 2, a first resist pattern is formed, andon it, a second resist pattern is formed. Subsequently, the secondresist is removed from a region at the first gap between ion conductingpart 4 and first electrode 1.

For example, for the first resist pattern, calixarene is used, and forthe second resist pattern, novolac resist is used, and thereby, thesecond resist pattern can be formed using an alkali aqueous solutionwithout destruction of the first resist pattern.

Next, on these resist, third electrode 3 is formed, and thereby thirdelectrode 3 can be formed to be in a convex shape in the region at thefirst gap between ion conducting part 4 and first electrode 1.

In addition, the metal atom migration switching device of the fourthembodiment may also include the insulator in gap 5, similarly to themetal atom migration switching device of the second embodiment. Further,block layer 8 shown in the third embodiment may be formed on the surfaceof ion conducting part 4 on the side of third electrode 3.

Fifth Embodiment

FIG. 8A is a schematic diagram illustrating a configuration of a fifthembodiment of a metal atom migration switching device having a gap andthree terminals according to the present invention. FIG. 8B is aschematic diagram illustrating growth of a precipitate that forms ametal wire between a first electrode and a second electrode shown inFIG. 8A.

As shown in FIG. 8A, the metal atom migration switching device of thefifth embodiment includes low-resistance insulating material 5 b at thefirst gap between ion conducting part 4 and first electrode 1, andhigh-resistance insulating material 5 a at the other region of gap 5.That is, it is different from the metal atom migration switching deviceof the first embodiment in the point that the insulator included in gap5 is configured to have a resistivity that is lower at the regionbetween the ion conducting part 4 and first electrode 1 than at anotherregion.

Because the metal atom migration switching device of the fifthembodiment includes the insulator in gap 5 similarly to the secondembodiment, it may be sufficient that the thickness of the first gap andthe second gap is about 1 nm to about 100 nm.

This difference generates a difference in operation of the metal atommigration switching device as described below. That is, when a negativevoltage relative to second electrode 2 is applied to third electrode 3,electrons which will reduce the metal ions near the surface of the ionconductor are directed to the first gap, including low-resistanceinsulating material 5 b, and so, most of which will reach the surface ofion conducting part 4 on the side of first electrode 1, and theyscarcely reach the surface of ion conducting part 4 on the side of thirdelectrode 3. As a result, the growth direction of precipitate 7 islimited to the direction from ion conducting part 4 to first electrode 1(see FIG. 8B).

Therefore, there is provided the advantage that wrong operation of themetal atom migration switching device (for example, operation in whichprecipitate 7 extends in the direction toward third electrode 3 to be incontact with third electrode 3) can be prevented. Further, as describedabove, it is advantageous, when the drive method, in which a voltagerelative to second electrode 2 is applied to third electrode 3, isadopted.

A method for manufacturing the metal atom migration switching device ofthe fifth embodiment is provided by changing the step of forming theresist (or insulating film) shown in FIG. 4B(g) to another step. In thefollowing description, the method for manufacturing the metal atommigration switching device of the fifth embodiment will be described inrelation to the case where gap 5 includes the resist, as an example, butit similarly applies to the case of the insulating film.

In the manufacturing method of this embodiment, after formation ofsecond electrode 2, photoresist (to form high-resistance material 5 a)is completely coated, and the photoresist is removed from an area exceptthe area of switching device and from a region for forming the first gapbetween ion conducting part 4 and first electrode 1, respectively, usingphotolithographic technique.

Next, conductive resist (to form low-resistance material 5 b) iscompletely coated, and the conductive resist is removed from the areaexcept the area of switching device using photolithographic technique.Subsequently, third electrode 3 is formed.

In addition, also in the metal atom migration switching device of thefifth embodiment, a block layer shown in the third embodiment may beformed on the surface of ion conducting part 4 on the side of thirdelectrode 3, and the thickness of the region corresponding to the firstgap between ion conducting part 4 and first electrode 1 in the first gapmay be formed to be thinner than that of the other region including thesecond gap as shown in the fourth embodiment.

Sixth Embodiment

FIG. 9A is a schematic diagram illustrating a configuration of a sixthembodiment of a metal atom migration switching device having a gap andthree terminals according to the present invention. FIG. 9B is aschematic diagram illustrating growth of a precipitate for forming ametal wire between a first electrode and a second electrode shown inFIG. 9A.

As shown in FIG. 9A, the metal atom migration switching device of thesixth embodiment is different from the metal atom migration switchingdevice of the first embodiment in the point that second electrode 2 isformed on the surface of ion conducting part 4 on the side of thirdelectrode 3.

Such a difference generates the following difference in operation of themetal atom migration switching device. That is, because second electrode2 is formed of dense, hard material such as Cu, precipitate 7 will notgrow to reach the inside of second electrode 2. As a result, the growthdirection of precipitate 7 is limited to the direction from ionconducting part 4 toward the first electrode.

Therefore, there is provided the advantage that wrong operation of themetal atom migration switching device (for example, an operation inwhich precipitate 7 extends in the direction toward third electrode 3 tobe in contact with third electrode 3) can be prevented. Further, asdescribed above, it is advantageous, when the drive method, in which avoltage relative to second electrode 2 is applied to third electrode 3,is adopted.

Further, in the metal atom migration switching device of the sixthembodiment, because second electrode 2 is laminated onto ion conductingpart 4, as the size of the metal wire composed of precipitate 7 thatgrows in the direction from ion conducting part 4 toward first electrode1 is increased, it is in contact with second electrode 2 as shown inFIG. 9B.

The ion conductor of ion conducting part 4 has smaller electricconductivity than that of metal. Therefore, connection between firstelectrode 1 and second electrode 2 through ion conducting part 4 has alarger on-resistance than that of direct connection through the metalwire composed of precipitate 7. Reduction in the on-resistance is a veryimportant advantage because of the consideration that reduction isspecially required for a switching device in order to diversifyfunctionality of the programmable logic and to promote implementation ofit in electric appliances (see the section of BACKGROUND ART).

A method for manufacturing the metal atom migration switching device ofthe sixth embodiment is such that, in the step of forming secondelectrode 2 shown in FIG. 4B(f), second electrode 2 is formed on ionconducting part 4 using a liftoff method.

In addition, the metal atom migration switching device of the sixthembodiment, similarly to the second embodiment, may also include theinsulator in gap 5. Further, the thickness of the region thatcorresponds to the first gap between ion conducting part 4 and firstelectrode 1 in the first gap may be formed thinner than that of theother region including the second gap as shown in the fourth embodiment,and the insulator also may be configured to have a lower resistivity atthe region between ion conducting part 4 and first electrode 1 than thatat the other region as shown in the fifth embodiment.

Seventh Embodiment

FIG. 10A is a schematic diagram illustrating a configuration of aseventh embodiment of a metal atom migration switching device having agap and three terminals according to the present invention. FIG. 10B isa schematic diagram illustrating growth of a precipitate for forming ametal wire between a first electrode and a second electrode shown inFIG. 10A.

As shown in FIG. 10A, the metal atom migration switching device of theseventh embodiment is different from the first embodiment in the pointthat ion conducting part 4 is formed on second electrode 2, and blocklayer 8 is formed on the surface of ion conducting part 4 on the side ofthird electrode 3. For block layer 8, dense, hard material such as SiO₂is preferably used.

This difference generates the following difference in operation of themetal atom migration switching device. That is, because block layer 8 isformed of dense, hard material such as SiO₂, precipitate 7 will not growinside of block layer 8. As a result, the growth direction ofprecipitate 7 is limited to the direction from ion conducting part 4toward first electrode 1.

This may provide the advantage that wrong operation of the metal atommigration switching device (for example, an operation in whichprecipitate 7 extends in the direction toward third electrode 3 to be incontact with third electrode 3) can be prevented. Further, as describedabove, it is advantageous, when the drive method, in which a voltagerelative to second electrode 2 is applied to third electrode 3, isadopted.

Further, in the metal atom migration switching device of the seventhembodiment, because ion conducting part 4 is laminated onto secondelectrode 2, as the size of the metal wire composed of precipitate 7that grows in the direction from ion conducting part 4 toward firstelectrode 1 is increased, it comes into contact with second electrode 2as shown in FIG. 10B.

The ion conductor of ion conducting part 4 has a smaller electricconductivity than that of metal. Therefore, connection between firstelectrode 1 and second electrode 2 through ion conducting part 4 has alarger on-resistance than that of a direct connection through the metalwire composed of precipitate 7 without ion conducting part 4. Reductionin the on-resistance is a very important advantage, because of theconsideration that a reduction is specially required for a switchingdevice in order to diversify functionality of the programmable logic andto promote implementation of it in electric appliances (see the sectionof BACKGROUND ART).

A method for manufacturing the metal atom migration switching device ofthe seventh embodiment is such that the order is reversed in which thestep of forming second electrode 2 using liftoff method shown in FIG.4B(f) and the step of forming ion conducting part 4 using liftoff methodshown in FIG. 4A(e) are carried out, and the step of forming block layer8 on ion conducting part 4 using liftoff method is added.

In addition, the metal atom migration switching device of the seventhembodiment, similarly to the second embodiment, may also include theinsulator in gap 5. Further, the thickness of the region correspondingto the first gap between ion conducting part 4 and first electrode 1 inthe first gap may be formed thinner than that of the other regionincluding the second gap as shown in the fourth embodiment, and theinsulator also may be configured to have a lower resistivity at theregion between ion conducting part 4 and first electrode 1 that is lowerthan that at the other region as shown in the fifth embodiment.

Eighth Embodiment

FIG. 11A is a schematic diagram illustrating a configuration of aneighth embodiment of a metal atom migration switching device having agap and three terminals according to the present invention. FIG. 11B isa schematic diagram illustrating growth of a precipitate for forming ametal wire between a first electrode and a second electrode shown inFIG. 11A.

As shown in FIG. 11A, the metal atom migration switching device of theeighth embodiment is configured in a manner such that ion conductingpart 4 composed of an ion conductor (Cu₂S) is formed on insulatingsubstrate 6 (SiO₂); and first electrode 1 (Pt) and second electrode 2(Cu) for supplying metal ions (Cu+) to ion conducting part 4, or forreceiving the metal ions (Cu+) from ion conducting part 4 to precipitatemetal (Cu) that corresponds to the metal ions, are disposed on ionconducting part 4 at a predetermined distance away from each other.

Further, on substrate 6, third electrode 3 is formed so as to have gap 5with ion conducting part 4. Gap 5 may be a vacuum, or filled with a gas.Alternatively, gap 5 may have an insulator. When gap 5 is the vacuum oris filled with the gas, it has a thickness of about 1 nm to about 10 nm.Further, when gap 5 has the insulator, it has a thickness of about 1 nmto about 100 nm. The thickness of ion conducting part 4 is about 10 nmto about 1,000 nm. First electrode 1 and second electrode 2 have athickness of about 1 nm to 100 nm, respectively, and are positioned at adistance of about 1 nm to 100 nm away from each other.

The metal atom migration switching device of the eighth embodiment has aconfiguration basically different from the metal atom migrationswitching devices described in the first to seventh embodiments. Thatis, the metal atom migration switching devices of the first to seventhembodiments are configured in a manner such that the first gap isprovided between ion conducting part 4 and first electrode 1, and ionconducting part 4 and first electrode 1 are not in contact with eachother. On the one hand, the metal atom migration switching device of theeighth embodiment is configured in a manner such that ion conductingpart 4 and first electrode 1 are in contact with each other.

As shown in FIG. 1B (see the section of BACKGROUND ART), if ionconducting part 4 is in contact with first electrode 1 and secondelectrode 2, it is believed that the metal atom migration switchingdevice having a gap is formed and precipitate 7 grows inside ionconducting part 4.

However, in the metal atom migration switching device of the eighthembodiment, since first electrode 1 and second electrode 2 are formed ata predetermined distance away from each other on ion conducting part 4,precipitate 7 will be precipitated at a region between first electrode 1and second electrode on a surface of ion conducting part 4.

If precipitate 7 is precipitated in this way on the surface of ionconducting part 4 between first electrode 1 and second electrode 2, whena negative voltage relative to second electrode 2 is applied to thirdelectrode 3, electrons, which will reduce the metal ions in the ionconductor (tunneling electrons, electrons thermally excited in theinsulator, and electrons created from impurities and defects), reach thesurface of ion conducting part 4 to contribute to an increase in thesize of the metal wire composed of precipitate 7.

That is, in the metal atom migration switching device of the eighthembodiment, ion conducting part 4 is in contact with first electrode 1and second electrode 2, but the metal atom migration switching device ofthe eighth embodiment is substantially the metal atom migrationswitching device having a gap and three terminals, similarly to themetal atom migration switching devices shown in the first to seventhembodiments.

In the metal atom migration switching device of the eighth embodiment,precipitate 7 grows only at a region between first electrode 1 andsecond electrode 2 on the surface of ion conducting part 4 (see FIG.11B).

Therefore, there is provided the advantage that wrong operation of themetal atom migration switching device (for example, an operation thatprecipitate 7 extends in the direction toward third electrode 3 to be incontact with third electrode 3) can be prevented. Further, as describedabove, it is advantageous, when the drive method, in which a voltagerelative to second electrode 2 is applied to third electrode 3, isadopted.

Further, in the eighth embodiment, first electrode 1 and secondelectrode 2 are connected to each other without ion conducting part 4.The ion conductor of ion conducting part 4 has a smaller electricconductivity than that of metal. Therefore, the connection between firstelectrode 1 and second electrode 2 through ion conducting part 4 has alarger on-resistance than that of a direct connection with the metalwire composed of precipitate 7 without ion conducting part 4.

Reduction in the on-resistance is a very important advantage, because ofthe consideration that a reduction is strongly required for a switchingdevice in order to diversify functionality of the programmable logic andto promote implementation of it in electric appliances (see the sectionof BACKGROUND ART).

The metal atom migration switching devices shown in the first to eighthembodiments can apply to the following apparatus or circuit.

For example, usage of the metal atom migration switching devicesaccording to the present invention as a programming device can provide aprogrammable integrated circuit device (programmable logic).

Further, a memory device can also be provided by using the metal atommigration switching device according to the present invention and atransistor for detecting whether the metal atom migration switchingdevice is in an on state or in an off state is provided.

1. A switching device, comprising: an ion conducting part having an ionconductor inside of which metal ions can move, a first electrode formedon said ion conducting part to be in contact with said ion conductingpart, a second electrode positioned on said ion conducting part at apredetermined distance away from said first electrode, for supplyingsaid metal ions to said ion conductor, or for receiving said metal ionsfrom the ion conductor to precipitate metal corresponding to the metalions, and formed to be in contact with the ion conducting part, and athird electrode formed to have a gap with the ion conducting part,wherein: when a negative voltage relative to said second electrode isapplied to said third electrode, a precipitate composed of said metalgrows at a region of said ion conducting part between said firstelectrode and said second electrode, and in response to growth of theprecipitate, electric characteristics change.
 2. The switching deviceaccording to claim 1, wherein: said change of electric characteristicsis a change in a state of conduction or non conduction between saidfirst electrode and said second electrode.
 3. The switching deviceaccording to claim 1, wherein: said predetermined distance is 1 nm to100 nm.
 4. The switching device according to claim 1, wherein: said ionconductor includes Cu₂S, a compound of a chalcogen element and metal, aninsulator including silicon, or a perovskite oxide.
 5. The switchingdevice according to claim 1, wherein: said metal includes Cu, Ag or Pb.6. The switching device according to claim 1, wherein: said firstelectrode and said third electrode include Pt, metal having ahigh-melting point or silicide.
 7. An integrated circuit device usingthe switching device according to claim 1 as a programming device.
 8. Amemory device, comprising: the switching device according to claim 1,and a transistor for detecting whether said switching device is in aconduction state or in a non conduction state.